Two other considerations:

1) How often and when (e.g., last minute or in advance) AM swaps aircraft. I don’t know the answer to this, but I do know that the only other aircraft capable of operating MEX-EZE, the 788, has a much inferior 2-2-2 configuration up front.
2) MEX-SFO is blocked at about an hour longer than IAH-SFO, so that’s about an hour more in a recliner than in a bed.